1. Field of the Invention
This invention relates to the use of plant oils to reduce pathogens and gaseous emissions from animal or human waste, particularly from excreta.
2. Description of the Prior Art
Livestock production and the waste generated can pose a threat to soil, water and air quality, and to human health. Some of the more serious problems with livestock waste include nutrient enrichment of soil and water, emission of odors and greenhouse gases, as well as presence and transmission of pathogenic microorganisms [Varel, V. H. et al. (1999), J Anim Sci 77:1162-1168].
Odor emitted from wastes results from an incomplete anoxic degradation of the carbohydrate, protein and lipid components [Mackie, R. I. et al. (1998), J. Anim. Sci. 76:1331-1342; Varel, V. H. et al. (1999), supra]. This incomplete degradation results in the formation of offensive short-chain volatile fatty acids, aromatic chemicals, amines and other nitrogenous compounds, and sulfur-containing compounds. In most of the livestock production facilities, it is not possible to control the environment whereby a complete degradation of the waste to methane and carbon dioxide occurs. Conventional anoxic digesters for production of methane were popular during the 1970's and 1980's; however, economics and technical expertise to operate them have diminished their popularity [Morse, D. et al. (1996) J. Dairy Sci. 79:149-153]. Similarly, oxic treatment is not economically feasible and it does little for conservation of nutrients.
Odor and greenhouse gas emissions are a direct result of microbial fermentation of waste [Mackie, R. I. et al. (1998), supra]. Thus, antimicrobial chemicals may be useful additives to waste to not only control the fermentation, but also destroy the pathogens [Varel, V. H. et al. (2001), Appl Environ Microbiol 67:1366-1370]. Naturally-occurring antimicrobial chemicals are desirable [Beuchat L R (1994), Antimicrobial properties of spices and their essential oils, p. 167-179. In V. M. Dillon and R. G. Board (ed.), Natural antimicrobial systems and food preservation. CAB International, Wallingford, England].
It was previously reported that chlorhexidine diacetate, in combination with iodoacetate or diphenyliodonium chloride, can be used to inhibit key anoxic degradation pathways [Varel, V. H. et al. (2000) Curr. Microbiol. 40:392-397]. Reduction of emissions by means of naturally occurring antimicrobial chemicals such as plant-derived oils has also been suggested [Beuchat, L. R. (1994), supra; Charai, M., M. et al. (1996), J. Essential Oil Res. 8:657-664; Dorman, H. J. D. et al. (2000), J. Appl. Bacteriol. 88:308-316; Helander, I. K. et al. (1998), J. Agric. Food Chem. 46:3590-3595; and Ultee, A. et al. (1999), Appl. Environ. Microbiol. 65:4606-4610]. Numerous reports indicate that plant oils have antimicrobial activity; however, most of these studies evaluate one oil against one microorganism in an artificial medium [Dorman et al. (2000), supra]. Few studies are available which determine the effect of the oils in natural highly diverse microbial ecosystems such as those found in the gastrointestinal tract [O'gara, E. A. et al. (2000), Appl. Environ. Microbial. 66:2269-2273], food products [Helander, I. K. et al. (1998), supra; Kim, J. M. et al. (1995), J. Food Sci. 60:1364-1374; and Skandamis, P. N. et al. (2000), Appl. Environ. Microbiol. 66:1646-1653] or waste management systems.
Numerous studies show that carvacrol and thymol are bactericidal to pathogens [Hammer, K. A. et al. (1999), J. Appl. Microbiol. 86:985-990; Kim, J. M. et al. (1995), J. Food Sci. 60:1364-1374; Pol, I. E. et al. (1999), Lett. Appl. Microbiol. 29:166-170; Ultee, A. et al. (1998), J. Appl. Microbiol. 85:211-218; and Ultee, A. et al. (1999), Appl. Environ. Microbiol. 65:4606-4610] and in particular to E. coli O157:H7 [Helander, I. K. (1998), supra); Kim, J. M. et al. (1995), J. Agric. Food Chem. 43:2839-2845; and Skandamis et al., supra] in pure culture. Helander et al. (supra) have shown that the minimum inhibitory concentration with carvacrol or thymol in a pure culture system is 3 mM and 1 mM for E. coli O157:H7 and Salmonella typhimurium, respectively. Kim et al. (supra) also found that 500 μg/ml (3.3 mM) of carvacrol will kill E. coli O157:H7. Also, previous studies have suggested that a combination of both thymol and carvacrol oils would provide better antimicrobial action, rather than a higher content of carvacrol or thymol alone [Manou, I. et al. (1998), J. Appl. Microbiol. 84:368-376; Paster, N. et al. (1995), J. Food Protect. 58:81-85].